Gastrointestinal tract

intestinegastrointestinaldigestive tractintestinesgutintestinalbowelalimentary canalgastrointestinal systemintestinal mucosa
The gastrointestinal tract (digestive tract, alimentary canal, digestion tract, GI tract, GIT) is an organ system within humans and other animals which takes in food, digests it to extract and absorb energy and nutrients, and expels the remaining waste as feces.wikipedia
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Mouth

oral cavityoralorally
The mouth, esophagus, stomach and intestines are part of the gastrointestinal tract.
It is also the cavity lying at the upper end of the alimentary canal, bounded on the outside by the lips and inside by the pharynx and containing in higher vertebrates the tongue and teeth.

Stomach

gastriccardiafundus
Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines. The GI tract includes all structures between the mouth and the anus, forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine.
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates.

Small intestine

small bowelsmall intestinessmall
The GI tract includes all structures between the mouth and the anus, forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine.
The small intestine or small bowel is an organ in the gastrointestinal tract where most of the end absorption of nutrients and minerals from food takes place.

Human digestive system

digestive systemdigestivedigestive tract
However, the complete human digestive system is made up of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder).
The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder).

Human mouth

mouthoral cavityfloor of mouth
The GI tract includes all structures between the mouth and the anus, forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine.
In human anatomy, the mouth is the first portion of the alimentary canal that receives food and produces saliva.

Organ (anatomy)

organorgansviscera
The gastrointestinal tract (digestive tract, alimentary canal, digestion tract, GI tract, GIT) is an organ system within humans and other animals which takes in food, digests it to extract and absorb energy and nutrients, and expels the remaining waste as feces.
A hollow organ is an internal organ that forms a hollow tube, or pouch such as the stomach, intestine, or bladder.

Foregut

fore-gutforegut developmentforegut tube
The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment.
The foregut is the anterior part of the alimentary canal, from the mouth to the duodenum at the entrance of the bile duct.

Anus

analperianalanal opening
In large bilaterians, the gastrointestinal tract also has an exit, the anus, by which the animal disposes of feces (solid wastes).
The anus (from Latin anus meaning "ring", "circle") is an opening at the opposite end of an animal's digestive tract from the mouth.

Midgut

mesenteronmidgut tissuesmidguts
The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment.
The midgut is the portion of the embryo from which most of the intestines develop.

Human gastrointestinal microbiota

gut floragut microbiotaintestinal flora
The gastrointestinal tract contains trillions of microbes, with some 4,000 different strains of bacteria having diverse roles in maintenance of immune health and metabolism.
Human gastrointestinal microbiota, also known as gut flora or gut microbiota, are the microorganisms that live in the digestive tracts of humans.

Bilateria

bilaterianbilateriansbilateral animals
All bilaterians have a gastrointestinal tract, also called a gut or an alimentary canal.
Except for a few phyla (i.e. flatworms and gnathostomulids), bilaterians have complete digestive tracts with a separate mouth and anus.

Smooth muscle

smooth muscle cellssmooth musclessmooth muscle cell
It is considerably shorter in the living body because the intestines, which are tubes of smooth muscle tissue, maintain constant muscle tone in a halfway-tense state but can relax in spots to allow for local distention and peristalsis.
Smooth muscle cells are found in the walls of hollow organs, including the stomach, intestines, urinary bladder and uterus, and in the walls of passageways, such as the arteries and veins of the circulatory system, and the tracts of the respiratory, urinary, and reproductive systems.

Liver

hepaticliver protein synthesislivers
However, the complete human digestive system is made up of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder).
The hepatic artery carries oxygen-rich blood from the aorta via the celiac plexus, whereas the portal vein carries blood rich in digested nutrients from the entire gastrointestinal tract and also from the spleen and pancreas.

Digestion

digestivedigestdigested
The gastrointestinal tract (digestive tract, alimentary canal, digestion tract, GI tract, GIT) is an organ system within humans and other animals which takes in food, digests it to extract and absorb energy and nutrients, and expels the remaining waste as feces. These digestive hormones, including gastrin, secretin, cholecystokinin, and ghrelin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.
Animals have a tube (gastrointestinal tract) in which internal digestion occurs, which is more efficient because more of the broken down products can be captured, and the internal chemical environment can be more efficiently controlled.

Ghrelin

cholinergic–dopaminergic reward linkGHRLghrelin, the "hunger hormone
These digestive hormones, including gastrin, secretin, cholecystokinin, and ghrelin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.
Ghrelin (pronounced /ˈɡrɛlɪn/), is a circulating hormone produced by enteroendocrine cells of the gastrointestinal tract, especially the stomach, and is often called a "hunger hormone" because it increases food intake.

Cholecystokinin

CCKpancreozymincholecystokinin (CCK)
These digestive hormones, including gastrin, secretin, cholecystokinin, and ghrelin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.
Cholecystokinin (CCK or CCK-PZ; from Greek chole, "bile"; cysto, "sac"; kinin, "move"; hence, move the bile-sac (gallbladder)) is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein.

Hindgut

hind-gut
The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment.
The hindgut (or epigaster) is the posterior (caudal) part of the alimentary canal.

Human anus

anusanalanal area
The GI tract includes all structures between the mouth and the anus, forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine.
The anus is the final component of the gastrointestinal tract, and directly continues from the rectum.

Peristalsis

peristalticgut motilityperistaltic contractions
It is considerably shorter in the living body because the intestines, which are tubes of smooth muscle tissue, maintain constant muscle tone in a halfway-tense state but can relax in spots to allow for local distention and peristalsis.
In much of a digestive tract such as the human gastrointestinal tract, smooth muscle tissue contracts in sequence to produce a peristaltic wave, which propels a ball of food (called a bolus while in the esophagus and upper gastrointestinal tract and chyme in the stomach) along the tract.

Large intestine

coloncolorectallarge bowel
The GI tract includes all structures between the mouth and the anus, forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine. In humans, the small intestine is further subdivided into the duodenum, jejunum and ileum while the large intestine is subdivided into the, cecum, ascending, transverse, descending and sigmoid colon, rectum, and anal canal.
The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates.

Rectum

rectalrectallyrectal ampulla
In humans, the small intestine is further subdivided into the duodenum, jejunum and ileum while the large intestine is subdivided into the, cecum, ascending, transverse, descending and sigmoid colon, rectum, and anal canal.
The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others.

Digestive enzyme

digestive enzymespancreatic enzymepancreatic enzymes
Digestive enzymes are found in the digestive tracts of animals (including humans) and in the tracts of carnivorous plants, where they aid in the digestion of food, as well as inside cells, especially in their lysosomes, where they function to maintain cellular survival.

Immune system

immuneimmune responseimmune function
The gastrointestinal tract contains trillions of microbes, with some 4,000 different strains of bacteria having diverse roles in maintenance of immune health and metabolism.
However, as organisms cannot be completely sealed from their environments, other systems act to protect body openings such as the lungs, intestines, and the genitourinary tract.

Human body

bodyhuman anatomyhuman physiology
In human anatomy, the intestine (bowel, or gut.
The body is also host to about the same number of non-human cells as well as multicellular organisms which reside in the gastrointestinal tract and on the skin.

Pancreas

pancreaticexocrine pancreaspancreatic development
However, the complete human digestive system is made up of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder).
As part of embryonic development, the pancreas forms as two buds from the foregut, an embryonic tube that is a precursor to the gastrointestinal tract.